1. Field of the Invention
The present invention relates to a kind of composite sheet structure that can be used as building and industrial material.
2. Description of the Related Art
Please refer to FIG. 1, representing a typical structure plan of traditional composite sheet, wherein the traditional composite sheet represents one kind of exterior cladding material in the building industry. The process of producing a traditional composite sheet includes the steps of (a) putting some plastic materials into an extruder which extrudes and heats the plastic materials (i.e. resin) until the plastic materials are melted; (b) the melted plastic materials are transported to a mold to become a flat core layer 1a of the composite sheet; (c) provide two metallic surfaces layers 2a to bond with the core layer 1a. 
As shown in FIG. 1, the structure of a traditional composite sheet includes the core layer 1a, and the two surface layers 2a. The core layer 1a is sandwiched between the two surface layers 2a. 
Because quantities of easily accessible natural resources (specifically metals) on Earth are decreasing, the cost of the composite sheet made of exotic metals will be more and more expensive. However, if we simply decrease the quantities of the more expensive metals for the metallic surface layers 2a and attempt to reduce the cost of the composite sheet in this simple fashion, the strength of the composite sheet would suffer and may not be enough to reach industry safety regulations.